I. Field of the Invention
Embodiments of this invention are directed generally to a process of making Zeolitic Imidazolate Framework materials and their use as membranes for separation of hydrocarbons.
II. Background
Zeolitic Imidazolate Frameworks (ZIFs) are a novel type of crystalline microporous materials. ZIFs are structurally similar to zeolites and other crystalline materials. ZIFs are comprised of metal ions or metal clusters bridged through a nitrogen atom of imidazolate ligands or their derivatives (Banerjee et al., Science, 2008, 319, P939), as compared to zeolites that are structures comprised of tetrahedral Si(Al)O4 joined by bridging oxygen. ZIFs belong to microporous materials because their pore size is typically less than 2 nm. The regular pore structure of ZIFs can differentiate gas molecules on the atomic level. Hence, ZIFs have potential to be used for gas separations, either in powder form or in a continuous membrane form.
US Patent Publication 2007/0202038, which is incorporated herein by reference in its entirety, describes synthesis of a family of ZIF materials and the methods of using them as adsorbents for H2 and CO2 storage. PCT Publication WO 2009/105270, which is incorporated herein by reference in its entirety, describes the use of ZIF crystals as adsorbents in a pressure swing or temperature swing process to recover H2 out of natural gas. PCT Publication WO 2009/105251, which is incorporated herein by reference in its entirety, describes different types of ZIF structures including ZIF-1, ZIF-7, ZIF-8 and ZIF-11 that were utilized as adsorbents to separate methane out of C2+ hydrocarbons. PCT Publication WO 2009/105251 also describes a membrane process based on these ZIF materials; however, the membrane described in WO 2009/105251 was prepared using ZIF crystals and binders. The separation mechanism is based on selective adsorption of C2+ over methane, and hence the membrane is more permeable to C2+ hydrocarbons.
There remains a need for additional materials for the sharp, efficient separation of multi-component gas mixtures.